Buffering

import { Grid } from 'cx/widgets';

Grid supports buffered rendering which dramatically improves performance with large datasets. Instead of rendering all rows, only visible rows plus a buffer are rendered, enabling smooth scrolling with thousands of records.

 <div controller={PageController}>
  <Grid
    records={m.records}
    keyField="id"
    buffered
    style="height: 400px"
    mod={["fixed-layout", "contain"]}
    cached
    selection={{ type: KeySelection, bind: m.selection }}
    columns={[
      {
        header: "#",
        align: "center",
        children: <div class="cxe-grid-row-number" />,
        defaultWidth: 70,
      },
      {
        header: { text: "Name", style: "width: 100%" },
        field: "fullName",
        sortable: true,
        resizable: true,
      },
      {
        header: "Continent",
        field: "continent",
        sortable: true,
        resizable: true,
        defaultWidth: 130,
      },
      {
        header: "Browser",
        field: "browser",
        sortable: true,
        resizable: true,
        defaultWidth: 100,
      },
      {
        header: "Visits",
        field: "visits",
        sortable: true,
        align: "right",
        resizable: true,
        defaultWidth: 70,
      },
    ]}
  />
</div> 
 class PageController extends Controller {
  onInit() {
    this.store.init(
      m.records,
      Array.from({ length: 5000 }, (_, i) => ({
        id: i + 1,
        fullName: names[i % 5],
        continent: continents[i % 5],
        browser: browsers[i % 5],
        visits: Math.floor(Math.random() * 100) + 1,
      })),
    );
  }
} 
 interface Record {
  id: number;
  fullName: string;
  continent: string;
  browser: string;
  visits: number;
}

interface PageModel {
  records: Record[];
  selection: number;
}

const m = createModel<PageModel>(); 
 import { createModel } from "cx/data";
import { Controller, KeySelection } from "cx/ui";
import { Grid } from "cx/widgets"; 

Name	Continent	Browser	Visits
Alice Johnson	North America	Chrome	35
Bob Smith	Europe	Firefox	45
Carol White	Asia	Safari	3
David Brown	South America	Edge	33
Eva Green	Africa	Opera	75
Alice Johnson	North America	Chrome	46
Bob Smith	Europe	Firefox	95
Carol White	Asia	Safari	87
David Brown	South America	Edge	28
Eva Green	Africa	Opera	29
Alice Johnson	North America	Chrome	29
Bob Smith	Europe	Firefox	100
Carol White	Asia	Safari	4
David Brown	South America	Edge	31
Eva Green	Africa	Opera	31
Alice Johnson	North America	Chrome	31
Bob Smith	Europe	Firefox	35
Carol White	Asia	Safari	89
David Brown	South America	Edge	59
Eva Green	Africa	Opera	59
Alice Johnson	North America	Chrome	53
Bob Smith	Europe	Firefox	62
Carol White	Asia	Safari	66
David Brown	South America	Edge	49
Eva Green	Africa	Opera	21
Alice Johnson	North America	Chrome	6
Bob Smith	Europe	Firefox	73
Carol White	Asia	Safari	81
David Brown	South America	Edge	34
Eva Green	Africa	Opera	57
Alice Johnson	North America	Chrome	20
Bob Smith	Europe	Firefox	17
Carol White	Asia	Safari	32
David Brown	South America	Edge	96
Eva Green	Africa	Opera	7
Alice Johnson	North America	Chrome	24
Bob Smith	Europe	Firefox	70
Carol White	Asia	Safari	87
David Brown	South America	Edge	58
Eva Green	Africa	Opera	41
Alice Johnson	North America	Chrome	18
Bob Smith	Europe	Firefox	24
Carol White	Asia	Safari	69
David Brown	South America	Edge	82
Eva Green	Africa	Opera	80
Alice Johnson	North America	Chrome	23
Bob Smith	Europe	Firefox	9
Carol White	Asia	Safari	3
David Brown	South America	Edge	3
Eva Green	Africa	Opera	95
Alice Johnson	North America	Chrome	66
Bob Smith	Europe	Firefox	17
Carol White	Asia	Safari	28
David Brown	South America	Edge	36
Eva Green	Africa	Opera	70
Alice Johnson	North America	Chrome	48
Bob Smith	Europe	Firefox	78
Carol White	Asia	Safari	57
David Brown	South America	Edge	99
Eva Green	Africa	Opera	60

This grid contains 5,000 rows but renders smoothly thanks to buffered mode. Try scrolling and sorting to see the performance.

How It Works

Enable buffered mode by setting the buffered property. The grid calculates which rows are visible and renders only those plus a configurable buffer for smooth scrolling.

<Grid
  records={m.records}
  buffered
  style="height: 400px"
  mod={["fixed-layout", "contain"]}
  cached
  columns={columns}
/>

For optimal performance, combine buffering with:

Fixed height - The grid needs a fixed height to calculate visible rows
mod="fixed-layout" - Uses CSS table-layout: fixed for faster rendering
mod="contain" - Adds CSS containment for better browser optimization
cached - Prevents row re-renders when unrelated store data changes

Row Numbers

Use the built-in cxe-grid-row-number class to display automatic row numbers:

{
  header: "#",
  defaultWidth: 50,
  children: <div class="cxe-grid-row-number" />
}

Configuration

Property	Type	Description
`buffered`	`boolean`	Enables buffered rendering mode.
`bufferSize`	`number`	Number of rows to render outside the visible area. Default is `60`.
`bufferStep`	`number`	Number of rows to add/remove when scrolling. Default is `15`.
`cached`	`boolean`	Prevents row re-renders when unrelated store data changes. Rows only update when their record data changes.
`lockColumnWidths`	`boolean`	Locks column widths to prevent layout shifts during scrolling.
`lockColumnWidthsRequiredRowCount`	`number`	Minimum number of rows required before column widths are locked.
`measureRowsOnScroll`	`boolean`	Re-measures row heights while scrolling. Useful for variable height rows.